SUMMARY:
UCLA researchers in the Department of Chemistry and Biochemistry have designed and developed a protein cage which can be easily tailored to sense other proteins, opening in response, and thus delivering enclosed biological compounds across a wide variety of applications, including biosensing, molecular diagnostics, and targeted drug delivery.
BACKGROUND:
Creating systems that can sense and respond or report on the presence of specific biological molecules is a major goal in medicine and biotechnology. This task, however, is nontrivial, due to the high structural complexity of biomolecules and the general difficulties in predicting their behaviors. Inspired by natural self-assembling biomolecules, such as protein capsids in bacterial cells, protein assemblies are emerging as a potential novel system for achieving molecular sensing. Recent bioengineering methods, many pioneered by the Yeates laboratory, have made it possible to create a diversity of self-assembling protein cages with novel compositions, shapes, structures, and ultimately, applications. However, typical protein cages must undergo lengthy re-engineering and design efforts for each new target protein. Thus, more facile and modular methods to adapt protein cages to sense different targets and elicit diverse responses could enhance and expand their utility in a wide variety of applications.
INNOVATION:
Researchers at UCLA led by Dr. Todd Yeates in the Department of Chemistry and Biochemistry have engineered a universal protein cage that is readily adapted for the sensing and responding to the presence of any target protein. Since they previously demonstrated the broad utility of structurally diverse protein cages, including applications in displaying enzymes or viral antigens on the surface and encapsulating nucleic acids, the researchers chose two specific structures, T33-31 and T33-51 to model their advancements. After attaching a ‘modular adaptor’ protein to the surface, they demonstrate via size exclusion chromatography that the cages remain stable in the absence of the target protein to which the adaptor was selected to bind, and expose their interior once the target protein binds. To enhance possibilities for dose-dependent responses, the researchers designed the construction such that the binding of a target protein to one adaptor protein causes it to either collide with neighboring cage subunits or with other copies of the target protein. Taken together, the universal protein cages offer a sense-and-respond system with broader applications.
POTENTIAL APPLICATIONS:
• A universally adaptable system for sensing and responding to a wide variety of target molecules for molecular diagnostics, biosensing, and in-situ biomarkers
• Protein cages can be designed to open and release various biological compounds or signaling molecules in applications such as targeted drug delivery
ADVANTAGES:
• Can be readily adapted for sensing of essentially any target protein
• Diverse modes of signaling upon cage opening, depending on the enclosed molecular species.
• Vast possibilities for the internal component, including drugs, nucleic acids, polypeptides, fluorescent motifs
• Unlimited architectural designs of protein cages that broaden their utility
DEVELOPMENT-TO-DATE:
The researchers have previously demonstrated the use of protein cages for various applications. Here, they used modeling and experimental tests to demonstrate a more advanced type of protein cage design, which critically introduces the capacity for cage-opening in response to diverse cellular proteins of interest, in a dose-dependent fashion. The researchers have demonstrated multiple types of readouts upon cage opening, including fluorescence unquenching and luminescence by enzyme complementation.